Preselector Gearboxes
The preselector gearbox was originally patented by Capt W.G.Wilson, and was used in production cars from around 1929. Racing cars were equipped with them from around 1931, and the MG Car Company used them in their K-series models of 1932-34. Unfortunately, they became criticisied for being unreliable and difficult to maintain. Both of these criticisms were unfair, the truth being that the garage trade did little to try and understand the workings of them, and preferred the conventional sliding gear transmissions. When synchromesh units were perfected, these provided a simpler answer to the difficulties of gear changing. It has to be admitted that preselectors are complicated in construction and not all that easy to work on, but to a properly trained engineer there are no problems. The sweetness of changing that can be achieved with these units has to be experienced to appreciate why preselectors enjoyed a vogue in more expensive carriages, and buses, which carried on right up to 1960, and really it was the advent of the fully automatic gearbox which resulted in their supercession.
MG cars were fitted with the ENV built 75 model, which was designed to deal with 75 lb.ft of torque maximum, buit is able to work with up to 100 if used sympathetically. Some developed MG racing cars were retrospectively fitted with the 110 model, or with an Armstrong-Siddeley built gearbox, but this work was carried out by or for owners outside the Factory.
Both of my cars are equipped with these delightful units, and back in the 1960's I was forced to find out how to rebuild them, and was given instruction by an ex-employee of Daimler, now long deceased. Basically they are a complicated piece of kit, and unless you are a competent engineer, do not even think about overhauling them yourself. However, if you want to know something about them I can always help you. I can give a practical courses, as detailed at the foot of this page. With each course, I will give a small handbook of notes, which was published in "The Pre-war MG Car, volume two, the six cylinder cars", but my leaflet if unpdated, this is included in the fee.
I have experience with ENV 75 and 110 units and Armstrong-Siddeley Riley, Autovia and A-S units, and have rebuilt examples from Talbot and Daimler, which differ in detail. I also went on a course with Borg Warner during my time at BMC, and spent a lot of time working on automatic gearboxes fitted to BMC cars. These are broadly similar in conception to the pre-war gearboxes, although the compression is hydraulic, rather than mechanical.
Alternatively, I am able to rebuild your unit for you.
One day course: How to strip a gearbox and inspect forrectification. £165
One day course: How to reassemble and preliminaryadjustments. £165
One day course: How to maintain gearbox, and running adjustments £165
Three day course: All three units, if booked and paid for in advance £450
All courses carried out at Newbury, by prior arrangement. Coffee, tea or soft drinks will be offered, but you will be responsible for your own lunch.
The courses will be carried out using your own gearbox, which should be brought complete, and drained of oil. For Course 2, you will need to have all the parts cleaned and ready for reassembly, with linigs attended to as agreed.